AI / Claude OPUS5 Interview questions
1. What is Claude Opus 5?
Claude Opus 5 is Anthropic's current Opus-tier model, positioned as an everyday, general-purpose model for coding, agentic work, and enterprise knowledge tasks, released July 24, 2026. It's designed to approach the intelligence of Anthropic's top-tier Claude Fable 5 model on many tasks while cost...
2. When was Claude Opus 5 released?
Claude Opus 5 was released on July 24, 2026, about eight weeks after Claude Opus 4.8, which itself had shipped on May 28, 2026 - a notably tighter release cadence than earlier Opus generations. Its launch came alongside two other platform updates on the same day: mid-conversation tool changes, le...
3. What is the pricing for Claude Opus 5?
Claude Opus 5 is priced at $5 per million input tokens and $25 per million output tokens, identical to the pricing of its predecessor, Claude Opus 4.8. A separate Fast mode, offered as a research preview, costs roughly double the standard rate - $10 per million input tokens and $50 per million ou...
4. What is the API model string for Claude Opus 5?
On the Claude API, Claude Opus 5 is addressed with the model string claude-opus-5 , replacing claude-opus-4-8 for teams migrating from the prior version. On Amazon Bedrock it's available as anthropic.claude-opus-5 , and it's also reachable through Bedrock's InvokeModel API on the same underlying ...
5. What is Claude Fable 5?
Claude Fable 5 is Anthropic's top-tier, frontier-intelligence model, sitting above the Opus tier and released as part of the same Mythos-tier generation as Claude Mythos 5. It shares its underlying model with Claude Mythos 5 but includes additional safety measures specific to biology, cybersecuri...
6. Describe the effort parameter in Claude Opus 5?
The effort parameter controls how much computational work Claude Opus 5 puts into a request - governing thinking depth as well as the depth of tool calls and arguments, not just visible response length - across levels typically described as low, medium, high, xhigh, and max. Claude Opus 5 default...
7. What is Fast mode for Claude Opus 5?
Fast mode is a research-preview option for Claude Opus 5 that trades higher per-token pricing for roughly 2.5 times faster output, aimed at exploration, drafting, and lower-risk loops where speed matters more than squeezing out maximum cost efficiency. It's currently available only through the Cl...
8. What is the context window size for Claude Opus 5?
Claude Opus 5 has a 1 million token context window, and that 1M figure is both the default and the absolute maximum - there's no smaller context-window variant to opt into instead. This matches the context window Claude Opus 4.8 and the Mythos-tier models, Fable 5 and Mythos 5, also use by defaul...
9. What is the maximum output token limit for Claude Opus 5?
Claude Opus 5 supports a maximum of 128,000 output tokens per response, the same ceiling used by its predecessor Opus 4.8. Because thinking now runs by default on Opus 5, and thinking tokens share the same max_tokens budget as the visible reply, a request that doesn't account for this can end up ...
10. Define thinking (reasoning) in the context of Claude Opus 5?
Thinking, also called reasoning, is Claude working through a problem step by step before producing its final answer, and on Claude Opus 5 it runs by default on every request rather than needing to be explicitly turned on. This is a first for the Opus model family - every Opus version before Opus ...
11. What is the prompt caching minimum for Claude Opus 5?
The minimum prompt length eligible for caching on Claude Opus 5 is 512 tokens, down from 1,024 tokens on Claude Opus 4.8. This means system prompts or other cacheable content that were previously too short to qualify for caching on Opus 4.8 can now create cache entries on Opus 5 automatically, wi...
12. Describe mid-conversation tool changes in Claude Opus 5?
Mid-conversation tool changes is a beta capability that lets developers add or remove tools available to Claude between turns of an ongoing conversation, without invalidating the prompt cache the way changing the tool list previously would have. Before this, an agentic session generally needed to...
13. What is automatic fallback on the Claude API?
Automatic fallback is a beta feature where API requests that get flagged by Claude Opus 5's or Claude Fable 5's safety classifiers can be automatically routed to another model instead of simply being blocked outright. With automatic fallback enabled, a request effectively always routes to the bes...
14. List the platforms where Claude Opus 5 is available?
Claude Opus 5 is available directly through the Claude API, as claude-opus-5 , through Amazon Bedrock, as anthropic.claude-opus-5 , through Claude on Google Cloud, as claude-opus-5 , and through Claude in Microsoft Foundry. It's also the default model on Claude Max and the strongest model selecta...
15. What is Claude Opus 5's position in Anthropic's Claude Max and Claude Pro plans?
On Claude Max, Anthropic's premium consumer subscription tier, Claude Opus 5 became the new default model upon release, replacing Claude Opus 4.8 in that role. On Claude Pro, Claude Opus 5 is the strongest model available to select, positioning it as the top consumer-facing option on that plan sp...
16. What is Claude Mythos 5?
Claude Mythos 5 shares the same underlying model as Claude Fable 5, both belonging to Anthropic's Mythos tier, which sits above the Opus tier in capability. The two differ mainly in safety posture: Fable 5 includes additional safety measures specific to biology, cybersecurity, and LLM R&D, while ...
17. How do you enable thinking on Claude Opus 5?
On Claude Opus 5, thinking is already enabled by default for requests that don't configure it explicitly, a change from every prior Opus model, where thinking needed to be explicitly turned on with something like thinking: {"type": "adaptive"} . Because of this, developers migrating from Opus 4.8...
18. What is the default effort level for Claude Opus 5?
Claude Opus 5 defaults to high effort on the API, which Anthropic positions as fitting most everyday coding and chat use cases without further tuning. This same high default is shared with Claude Fable 5, so both models start from a comparable baseline of effort unless a request explicitly dials ...
19. Describe subagent delegation in Claude Opus 5?
Subagent delegation refers to Claude Opus 5's tendency, during agentic work, to hand off portions of a task to subagents more readily than earlier Opus models did. This is one of the behavioral shifts Anthropic's own prompting guidance calls out as worth checking when moving a workflow from Opus ...
20. How do you migrate an application from Claude Opus 4.8 to Claude Opus 5?
The baseline step is simple: change the model identifier from claude-opus-4-8 to claude-opus-5 in API requests, since most existing requests continue to work without further changes. Beyond that string swap, it's worth explicitly checking a small number of behavior changes that can affect correct...
21. What is the difference between Claude Opus 5 and Claude Opus 4.8?
The most consequential functional difference is that Claude Opus 5 runs with thinking on by default, while Opus 4.8 ran without thinking unless a request explicitly enabled it - this alone changes both typical token cost and answer quality on unconfigured requests. Opus 5 also lowers the prompt-c...
22. How does Claude Opus 5 compare to Claude Fable 5 in capability and price?
Anthropic positions Claude Opus 5 as approaching Fable 5's frontier intelligence on many everyday tasks while costing roughly half as much, making it the more cost-efficient default choice for typical coding, analysis, and business-automation work. On specific published benchmarks, the gap narrow...
23. Why is thinking on by default a breaking change when migrating to Claude Opus 5?
Because max_tokens caps thinking and the visible reply together as one shared budget, a request that previously produced no thinking at all on Opus 4.8 now consumes part of that same budget on thinking before Opus 5 even starts on the visible answer. If an application's max_tokens value was tuned...
24. What is the difference between the effort parameter and response verbosity in Claude Opus 5?
The effort parameter controls how much Claude Opus 5 thinks, and by extension how deep its reasoning, tool calls, and argument construction go - it's fundamentally about internal computational work, not the length of the final visible answer. Response verbosity, the actual length of what the user...
25. When should you use Fable 5 instead of Opus 5?
Reach for Fable 5 when a task is at the edge of what's currently possible - the most demanding reasoning, or the largest and most ambiguous multi-day autonomous agentic projects - where Opus 5's slightly smaller capability margin relative to Fable 5 is more likely to actually matter to the outcom...
26. How does Claude Opus 5's self-verification behavior differ from Claude Opus 4.8?
Claude Opus 5 verifies its own work unprompted more consistently than Opus 4.8 did, meaning it's more likely to catch and correct its own mistakes without an explicit instruction telling it to double-check. This creates a specific migration trap: verification instructions written for Opus 4.8, li...
27. What is the difference between disabling thinking on Opus 5 vs Fable 5?
On Claude Opus 5, thinking can be explicitly disabled with thinking: {"type": "disabled"} , but only at effort level high or below - attempting this at xhigh or max effort returns an HTTP 400 error, since those higher effort levels require thinking to stay on. On Claude Fable 5 and Claude Mythos ...
28. Why does max_tokens behave differently on Claude Opus 5 compared to Claude Opus 4.8?
On Claude Opus 4.8, a request that didn't explicitly enable thinking produced no thinking tokens at all, so the full max_tokens budget was effectively available to the visible reply by default. On Claude Opus 5, thinking runs by default for the same kind of unconfigured request, and thinking toke...
29. How does Claude Opus 5's narration behavior affect agentic prompting?
Claude Opus 5 tends to narrate more during agentic work than earlier models - announcing what it's about to do before taking an action - and its per-message output during agentic sessions tends to run longer as a result. Left unguided, this can make agent transcripts noisier than teams may want, ...
30. What is the difference between Opus 5 and Opus 4.8 rate limits?
Claude Opus 5 draws on its own separate rate-limit bucket, distinct from the combined pool that Opus 4.x models, like 4.6, 4.7, and 4.8, share together. This means shifting traffic from Opus 4.8 over to Opus 5 doesn't free up headroom on the old shared Opus 4.x bucket, and it also doesn't automat...
31. When should you use Fast mode for Claude Opus 5?
Fast mode suits exploration, rapid drafting, and lower-risk iterative loops where getting a response back quickly matters more than minimizing cost per token, since it runs at roughly 2.5 times the speed of standard mode at about double the price. It's less suited to workloads where cost efficien...
32. How does Opus 5 handle disabling thinking at xhigh or max effort?
Claude Opus 5's API rejects this specific combination outright: setting thinking: {"type": "disabled"} together with effort xhigh or max returns an HTTP 400 error rather than silently ignoring the disable request or falling back to some default behavior. This is a deliberate restriction - Anthrop...
33. What is the difference between Claude Opus 5's Priority Tier support and Claude Opus 4.8's?
Claude Opus 4.8 supported Priority Tier, a paid enterprise feature some teams relied on for their traffic, while Claude Opus 5 does not support Priority Tier at all. This is a concrete capability regression to account for during migration - enterprise teams paying for Priority Tier on Opus 4.8 tr...
34. Why should you avoid carrying over "double-check your work" instructions to Claude Opus 5?
Claude Opus 5 already performs self-verification on its own by default, more consistently than Opus 4.8 did, so an explicit "double-check your work" instruction that was useful on the older model now layers on top of behavior the model is already doing unprompted. The practical result is over-ver...
35. How does Claude Opus 5's prompt caching minimum affect short system prompts?
Because the minimum cacheable prompt length dropped from 1,024 tokens on Opus 4.8 to 512 tokens on Opus 5, system prompts that fell in that 512-1,024 token range - too short to cache before - now qualify for caching automatically. This applies with no code changes required: simply moving the same...
36. How do Opus 5 and Fable 5 differ in calibrating thinking depth?
Both models use the effort parameter, alongside query complexity, to calibrate how much thinking actually happens on a given turn, and both share the same high default effort level. The key structural difference is that Opus 5 allows thinking to be explicitly disabled, at effort high or below, wh...
37. When should you scope, rather than remove, a verification instruction?
Scope a verification instruction to a specific step, rather than removing all verification instructions outright, when that particular step carries meaningfully higher stakes or risk than the rest of the task - somewhere a mistake would be especially costly to miss even given Opus 5's generally s...
38. How does Opus 5's release cadence compare to Opus 4.5 and 4.1?
Anthropic's Opus releases accelerated notably over this period: Opus 4.1 shipped around August 2025, Opus 4.5 followed roughly three months later in November 2025, and subsequent versions, 4.6, 4.7, 4.8, arrived in progressively tighter succession, with Opus 4.8 landing May 28, 2026, just 41 days...
39. Explain how the effort parameter governs Claude Opus 5's output beyond just reasoning?
Effort doesn't only scale how much internal reasoning Claude Opus 5 performs before answering - it governs essentially every token the model produces during a turn, including the depth of tool calls it makes and how much elaboration goes into constructing tool arguments, not just the thinking blo...
40. How can you optimize prompts when migrating from Opus 4.8 to Opus 5?
Start by testing existing Opus 4.8 prompts as-is, since Anthropic reports Opus 5 performs well out of the box on them - this isn't a full prompt rewrite, but a targeted tuning pass on a specific, known set of behaviors. Add an explicit conciseness instruction if your product depends on a particul...
41. How do you troubleshoot an Opus 5 response truncated at max_tokens?
First confirm whether thinking is running on the affected request - since Opus 5 runs thinking by default, and thinking tokens share the same max_tokens budget as the visible reply, this is the most likely cause if the same request and max_tokens value worked fine on Opus 4.8 without truncation. ...
42. Explain the execution flow of mid-conversation tool changes in Claude Opus 5?
In a standard agentic session prior to this feature, the tool list provided in a request needed to stay fixed for the life of the conversation - changing which tools were available on a later turn would invalidate the prompt cache built up from earlier turns, forcing an expensive cache miss. With...
43. How can you optimize agentic narration behavior in Claude Opus 5 through prompting?
Rather than issuing a blanket "don't narrate" instruction, which Anthropic's guidance suggests is less effective, describe the specific cadence you actually want: for example, one sentence before the first tool call to set expectations, brief updates only when something important surfaces or the ...
44. Which is better for long-horizon autonomous coding: Opus 5 or Fable 5?
For a task genuinely at this scale and duration, Anthropic's own guidance points toward Fable 5 as the recommended choice, since it explicitly calls out Fable 5 as better suited to more advanced projects, including ones a model may handle autonomously over multiple days, while positioning Opus 5 ...
45. How do you troubleshoot an HTTP 400 error disabling thinking on Opus 5?
Check the effort level configured on the failing request first - this specific error occurs when thinking: {"type": "disabled"} is combined with effort xhigh or max, since Claude Opus 5 requires thinking to remain enabled at those two highest effort levels. If the workload genuinely needs xhigh o...
46. Explain the tradeoffs of using Claude Opus 5's Fast mode versus standard mode?
Fast mode trades roughly double the per-token price, $10 input/$50 output versus $5/$25 on standard, for approximately 2.5 times faster output, a meaningfully different cost-speed tradeoff curve than simply raising or lowering the effort parameter on standard mode. Because it's currently a resear...
47. How can you optimize cost migrating high-volume workloads to Opus 5?
Take advantage of the lower prompt-caching minimum, 512 tokens versus 1,024 on Opus 4.8, by checking whether previously-uncacheable short system prompts now qualify automatically, since this can reduce cost with literally no code changes for workloads that reuse a consistent, short system prompt ...
48. Explain the artifacts that can appear in Claude Opus 5's output when thinking is disabled?
With thinking disabled, at effort high or below, Claude Opus 5 can occasionally write what should have been a structured tool call directly into its user-facing text output instead of emitting a proper tool_use block - the turn completes normally, but the intended tool call never actually runs. T...
49. How do you troubleshoot over-verification behavior in a Claude Opus 5 agentic workflow?
Start by auditing the prompt for verification instructions carried over from an Opus 4.8 setup - a blanket "double-check your work" or similar global instruction is the most common source, since it compounds with Opus 5's stronger built-in self-verification rather than adding proportional value. ...
50. Explain how Opus 5's positioning versus Fable 5 reflects Anthropic's strategy?
Opus 5's design, approaching Fable 5's intelligence on many tasks at roughly half the price, alongside a tunable effort parameter that lets teams trade capability for cost on a sliding scale, reflects a strategic shift Anthropic has been signaling: that competition in AI is moving from purely cha...
