Feature + DeadlineReleased 30 October 2026 · 3 min read
Fast Opus 4.8 requests return errors from 30 November.
Anthropic has deprecated fast mode for Claude Opus 4.8 and will remove it on 30 November 2026. After removal, any request to claude-opus-4-8 with speed: "fast" returns an error. Anthropic says that to keep using fast mode, you migrate to Claude Opus 5.5.
Opus 4.8 fast mode is removed in
31 days
30 Nov 2026 · claude-opus-4-8 with speed: "fast"
- Deprecated
- Fast mode on Claude Opus 4.8
- Removal date
- 30 November 2026
- After removal
- speed: "fast" returns error
- Model ID affected
- claude-opus-4-8
- To keep fast mode
- Migrate to Claude Opus 5.5
Timeline
- Fast mode removed; claude-opus-4-8 requests with speed: "fast" return an error
01 · What changed
One deprecation, one date.
What changed: Anthropic's Claude Platform release notes mark fast mode on Claude Opus 4.8 as deprecated, with removal on 30 November 2026. The change sits in the API request. A call that names claude-opus-4-8 and sets speed: "fast" will fail once fast mode is removed. Any tool built on that combination, such as an inbound email triage step or a first-pass read of a data room, needs to move to Claude Opus 5.5 before then if it is to keep running in fast mode.
Removal date
30 Nov 2026
Anthropic removes fast mode for Claude Opus 4.8 on this date.
After removal
Error
Requests to claude-opus-4-8 with speed: "fast" return an error.
Migration path
Opus 5.5
Anthropic says to migrate to Claude Opus 5.5 to continue using fast mode.
02 · What it means
What it means for your seat.
Any internal tool or vendor integration that sends fast-mode requests to Claude Opus 4.8 has until 30 November 2026 to change. After that date those requests fail, and the step that depended on them stops returning output. The work is to find those requests, test the same tasks on Claude Opus 5.5 and switch before the removal date.
Leadership
Ask your technology lead whether anything the firm relies on calls Claude Opus 4.8 in fast mode. If a tool that drafts a first pass of an IC memo or triages inbound investor email uses it, that tool needs to move to Claude Opus 5.5 before 30 November 2026. Make sure someone owns the change and has a date for it.
Operations
List the workflows where a failed request would show up first, such as a weekly status report that is generated automatically or an email triage queue. Find out which of them run on Claude Opus 4.8 in fast mode and who maintains each one. Agree when each will be switched and tested, well before 30 November.
Risk and compliance
Moving a workflow from Claude Opus 4.8 to Claude Opus 5.5 is a model change, so treat it like one. Run the outputs through the same review you applied when the workflow was approved, for example on a credit agreement summary or a board pack draft. Record which model each approved workflow now uses and when it changed.
IT and engineering
Search code, configuration and environment variables for claude-opus-4-8 used with speed: "fast". After 30 November 2026 those requests return an error, so plan the move to Claude Opus 5.5 now. Check Anthropic's Fast mode documentation for the exact model ID and parameters before you change anything.
03 · Before 30 November
Migration checklist.
0 of 3 done
Sources
Facts and dates are Anthropic’s own. What it means and what to do are our view, from the firms we work with. Drafted with Claude from these sources, checked against them figure by figure, and published 30 October 2026.
The short answers.
When is fast mode for Claude Opus 4.8 removed?
Anthropic will remove fast mode for Claude Opus 4.8 on November 30, 2026. Anthropic announced the deprecation in its Claude Platform release notes.
What happens to Claude Opus 4.8 fast mode requests after November 30, 2026?
After removal, requests to claude-opus-4-8 with speed: "fast" return an error. Any workflow that sends those requests will stop getting a response from the model.
How do I keep using fast mode after Opus 4.8 fast mode is removed?
Anthropic says to migrate to Claude Opus 5.5 to continue using fast mode. Check Anthropic's Fast mode documentation for the details before switching.
Is Claude Opus 4.8 itself being retired?
The release note covers fast mode on Claude Opus 4.8 only and does not give a retirement date for the model. It states that requests to claude-opus-4-8 with speed: "fast" will return an error after November 30, 2026.
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Need help moving off Opus 4.8 fast mode?
We help firms find the workflows that call Claude Opus 4.8 in fast mode, test them on Claude Opus 5.5 with the people who review the output, and switch before 30 November 2026.