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What is Claude Opus 4.5?

Claude Opus 4.5 is Anthropic's reasoning model for coding, agents and complex knowledge work, released November 24, 2025. Its pinned API ID is claude-opus-4-5-20251101; the alias is claude-opus-4-5. It accepts text and images and returns text. Checked September 8, 2026: the latest released Opus is Claude Opus 5, launched July 24, 2026. The Opus product page still heads with 4.8 while its announcement and availability sections describe 5. This page stays with 4.5, which remains documented as available.

What the 4.5 API supports

A 200K working context: The 4.5 API overview lists 200K context tokens and a 64K output maximum. Reserve room for the answer and tool results. For a repository or document collection, select relevant files and preserve source references instead of assuming everything will fit.
Reasoning effort you can evaluate: Opus 4.5 uses extended thinking. Its effort control offers low, medium and high; high is the default. Effort influences explanations, tool calls and thinking, not a fixed spending cap. Test a lower setting on routine work and retain deeper reasoning where it improves the verified result.
Price the completed task: Standard provider rates are USD $5 per million input tokens and $25 per million output tokens. A 10,000-input, 2,000-output request is $0.10 before caching, tools and other adjustments. These are not Ottermind prices. Repeated attempts and human review can matter more than the price of a single answer.

Work worth testing with Opus 4.5

Its strongest reason for consideration is a problem with interacting constraints. Use these bounded tasks to decide whether its extra reasoning helps your work.

Untangle a cross-system bug
Provide request IDs, logs from each service and the last known good behavior. Ask for a timeline, competing causes and a test that distinguishes them before requesting a patch. This helps separate an API fault from stale client state or a retry that applies an operation twice.
Plan a migration without losing behavior
Share the old and new interfaces, compatibility requirements and representative tests. Request a staged migration with rollback points, then implement one boundary at a time. Check callers and data formats as well as compilation so a tidy refactor does not silently change the contract.
Reconcile documents into a decision
Attach dated proposals, meeting notes and the criteria for a decision. Ask for disagreements, supporting passages and the assumptions behind each option. Review the source of every recommendation; a fluent synthesis can otherwise hide an unresolved conflict between two documents.
Inspect a spreadsheet's assumptions
Provide column definitions, sample rows, formulas and expected totals. Ask where units, missing values or duplicated records could change the conclusion. Recalculate the proposed corrections in your spreadsheet tool; a plausible explanation is not evidence that the workbook was executed.

Claude Opus 4.5 vs Claude Opus 5

Decision point	Claude Opus 4.5	Claude Opus 5
Standard API input / output	USD $5 / $25 per million tokens	USD $5 / $25 per million tokens
Context / maximum output	200K / 64K tokens	1M / 128K tokens
Thinking	Extended thinking	Adaptive thinking
Reason to evaluate	Preserve a tested 4.5 workflow or reproduce prior results	Test the current Opus on longer inputs and the same acceptance cases

When keeping 4.5 makes sense

Reasons to evaluate it

A known behavior baseline: Existing prompts, accepted patches and reviewed documents give you a useful 4.5 baseline. Keep representative failures too. That lets you measure a replacement against your actual workload rather than judge it only by a polished first answer.
Planning linked to the next action: Use the analysis to produce a bounded implementation brief, a source-backed memo or a list of spreadsheet checks. Ottermind connects that brief to the next stage of work. Model and tool availability depends on your account; the page itself does not establish access.

Tradeoffs to measure

An older model is not cheaper by default: The Opus 5 API overview lists the same base token rates and a larger window. If you have no dependency on 4.5 behavior, evaluate 5 as well. Compare accepted results, elapsed time and total tokens; equal rates do not mean equal task costs.
More reasoning can become extra work: For a narrow edit, expansive planning or speculative edge cases may delay the result and enlarge the diff. State the allowed scope and ask for evidence before additional changes. Stop repeated repair attempts when they fail to change the observed bug.

What users found in practice

These discussions offer individual reports from the 4.5 launch period and following weeks, not a consensus or a current controlled benchmark. The client, task and subscription affect the experience.

Fewer retries may outweigh the token price

In the Hacker News launch discussion, an Amp team member reported lower early average thread costs with Opus 4.5 than Sonnet 4.5 in their internal usage. That is an affiliated, uncontrolled observation. It supports measuring cost per finished task, not promising savings for every user.

Small UI fixes can still take several tries

In a non-coder's experience report, the author describes six attempts to fix a horizontal filter's scroll position and faster quota depletion. Replies disagree: some value Opus for unfamiliar problems, while others prefer Sonnet for precise instructions. A screenshot and a convincing answer are not substitutes for reproducing the interaction.

Continue the work in Ottermind

Prepare the evidence

Include the failure, relevant sources and constraints. Specify the output you need, such as a diagnosis with a reproduction, a migration sequence or a memo with source passages.

Confirm availability in Studio

Continue to Studio and sign in if needed. Select Claude Opus 4.5 if available to your account and check usage terms. This page does not automatically select the model or guarantee access.

Check the result before using it

Run the reproduction, inspect the diff or recalculate the numbers. Keep the accepted findings and unresolved questions together so the next step can build on work you have verified.

Claude Opus 4.5 FAQ

Is Opus 4.5 retired or still available?

As of September 8, 2026, the overview labels it Legacy, and the lifecycle table lists Active with retirement not sooner than November 24, 2026. That is not an announced shutdown date. Check your provider before depending on continued access.

Does Opus 4.5 have Opus 5's larger context?

No. The documented 4.5 limits are 200K context and 64K maximum output. The 1M context, 128K output and adaptive thinking in the comparison belong to Opus 5. Product updates do not change the identity of the pinned 4.5 model.

Can it browse or edit a spreadsheet by itself?

Its native output is text. Browsing, running code and editing files require tools supplied by the application. Image input can support visual analysis, but it neither generates images natively nor proves a workbook was opened and recalculated.

Does this page include free Opus 4.5 access?

No free usage or model availability is promised. Your prompt continues into Studio, where access, tools and charges depend on your account. Confirm the available model before starting.

Give a difficult task a checkable next step

Bring your evidence into Ottermind Studio and turn the analysis into a result you can inspect, test and continue.