A disableFastMode breaker exists with no local default, so it never fires without server config.
What
A new circuit breaker disables auto mode with the reason "fast-mode" when the remote tengu_auto_mode_config object sets disableFastMode and you have /fast toggled on. There is no local fallback value for disableFastMode, so with no server config it is undefined and the breaker never fires. This replaces the old branch that blocked auto mode for providers lacking an opt-in.
Details
- The debug output now reports a
disableFastModeBreakerFirescounter.
Evidence
auto mode disabled: tengu_auto_mode_config.disableFastMode with the /fast toggle on
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
Names in the bundle/fast
Feature flag
tengu_auto_mode_config Not enough to sayNothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.
This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.248: not a boolean we can read
Read once, for one account on one subscription tier, against v2.1.248. It isn't a statement about your account. What a flag value here can and cannot tell you
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed since
Anthropic's documentation has since written up /fast, on Extension Support Matrix.
| [fast-agent](https://github.com/evalstate/fast-agent) | | | | [Partial](https://github.com/evalstate/fast-agent/blob/main/docs/docs/mcp/skills-over-mcp.md) |extensions/client-matrix see the edit
Added since
A small documentation edit on Speed up responses with fast mode touched a line naming /fast after this was published.
* **Usage credits turned on for subscription plans**: on a Pro, Max, Team, or Enterprise plan, your account must have [usage credits](/docs/en/costs#add-usage-credits-to-your-subscription) turned on, which allows billing beyond your plan's…fast-mode see the edit
Flag reading moved
The flag server now returns {"editRemovalCap":3000,"editRemovalVisibility":true,"enabled":"enabled","envOnboarding":true,"gitStatusType":true,"gitStatusUploads":false,"jsonlTranscript":true,"outcomeVisibility":false,"repoVisibility":true,"sameTurnSiblingContext":true,"severityByModel":{"claude-opus-4-8":{"t1":45,"t2":35},"claude-opus-4-8[1m]":{"t1":45,"t2":35},"claude-sonnet-5":{"t1":25,"t2":35},"claude-sonnet-5[1m]":{"t1":25,"t2":35}},"severityBySite":{"compactFabCheck":"on","handoff":"on","investigator":"on","sandboxNetwork":"on","workflowGate":"on"},"twoStageClassifier":true} for tengu_auto_mode_config, read as this account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading moved
The flag server now returns {"editRemovalCap":3000,"editRemovalVisibility":true,"enabled":"enabled","envOnboarding":true,"gitStatusType":true,"gitStatusUploads":false,"jsonlTranscript":true,"modelByMainModel":{"claude-haiku-5-5":"claude-sonnet-5[1m]","claude-haiku-5-5[1m]":"claude-sonnet-5[1m]"},"outcomeVisibility":false,"repoVisibility":true,"sameTurnSiblingContext":true,"severityByModel":{"claude-opus-4-8":{"t1":45,"t2":35},"claude-opus-4-8[1m]":{"t1":45,"t2":35},"claude-sonnet-5":{"t1":25,"t2":35},"claude-sonnet-5[1m]":{"t1":25,"t2":35}},"severityBySite":{"compactFabCheck":"on","handoff":"on","investigator":"on","sandboxNetwork":"on","workflowGate":"on"},"twoStageClassifier":true} for tengu_auto_mode_config, read as this account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading moved
The flag server now returns {"editRemovalCap":3000,"editRemovalVisibility":true,"enabled":"enabled","envOnboarding":true,"gitStatusType":true,"gitStatusUploads":false,"jsonlTranscript":true,"outcomeVisibility":false,"repoVisibility":true,"sameTurnSiblingContext":true,"severityByModel":{"claude-opus-4-8":{"t1":45,"t2":35},"claude-opus-4-8[1m]":{"t1":45,"t2":35},"claude-sonnet-5":{"t1":25,"t2":35},"claude-sonnet-5[1m]":{"t1":25,"t2":35}},"severityBySite":{"compactFabCheck":"on","handoff":"on","investigator":"on","sandboxNetwork":"on","workflowGate":"on"},"twoStageClassifier":true} for tengu_auto_mode_config, read as this account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading moved
The flag server now returns {"editRemovalCap":3000,"editRemovalVisibility":true,"enabled":"enabled","envOnboarding":true,"gitStatusType":true,"gitStatusUploads":false,"jsonlTranscript":true,"modelByMainModel":{"claude-haiku-5-5":"claude-sonnet-5[1m]","claude-haiku-5-5[1m]":"claude-sonnet-5[1m]"},"outcomeVisibility":false,"repoVisibility":true,"sameTurnSiblingContext":true,"severityByModel":{"claude-opus-4-8":{"t1":45,"t2":35},"claude-opus-4-8[1m]":{"t1":45,"t2":35},"claude-sonnet-5":{"t1":25,"t2":35},"claude-sonnet-5[1m]":{"t1":25,"t2":35}},"severityBySite":{"compactFabCheck":"on","handoff":"on","investigator":"on","sandboxNetwork":"on","workflowGate":"on"},"twoStageClassifier":true} for tengu_auto_mode_config, read as this account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading moved
The flag server now returns {"editRemovalCap":3000,"editRemovalVisibility":true,"enabled":"enabled","envOnboarding":true,"gitStatusType":true,"gitStatusUploads":false,"jsonlTranscript":true,"outcomeVisibility":false,"repoVisibility":true,"sameTurnSiblingContext":true,"severityByModel":{"claude-opus-4-8":{"t1":45,"t2":35},"claude-opus-4-8[1m]":{"t1":45,"t2":35},"claude-sonnet-5":{"t1":25,"t2":35},"claude-sonnet-5[1m]":{"t1":25,"t2":35}},"severityBySite":{"compactFabCheck":"on","handoff":"on","investigator":"on","sandboxNetwork":"on","workflowGate":"on"},"twoStageClassifier":true} for tengu_auto_mode_config, read as this account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading moved
The flag server now returns {"editRemovalCap":3000,"editRemovalVisibility":true,"enabled":"enabled","envOnboarding":true,"gitStatusType":true,"gitStatusUploads":false,"jsonlTranscript":true,"modelByMainModel":{"claude-haiku-5-5":"claude-sonnet-5[1m]","claude-haiku-5-5[1m]":"claude-sonnet-5[1m]"},"outcomeVisibility":false,"repoVisibility":true,"sameTurnSiblingContext":true,"severityByModel":{"claude-opus-4-8":{"t1":45,"t2":35},"claude-opus-4-8[1m]":{"t1":45,"t2":35},"claude-sonnet-5":{"t1":25,"t2":35},"claude-sonnet-5[1m]":{"t1":25,"t2":35}},"severityBySite":{"compactFabCheck":"on","handoff":"on","investigator":"on","sandboxNetwork":"on","workflowGate":"on"},"twoStageClassifier":true} for tengu_auto_mode_config, read as this account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading moved
The flag server now returns {"editRemovalCap":3000,"editRemovalVisibility":true,"enabled":"enabled","envOnboarding":true,"gitStatusType":true,"gitStatusUploads":false,"jsonlTranscript":true,"outcomeVisibility":false,"repoVisibility":true,"sameTurnSiblingContext":true,"severityByModel":{"claude-opus-4-8":{"t1":45,"t2":35},"claude-opus-4-8[1m]":{"t1":45,"t2":35},"claude-sonnet-5":{"t1":25,"t2":35},"claude-sonnet-5[1m]":{"t1":25,"t2":35}},"severityBySite":{"compactFabCheck":"on","handoff":"on","investigator":"on","sandboxNetwork":"on","workflowGate":"on"},"twoStageClassifier":true} for tengu_auto_mode_config, read as this account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
Flag reading moved
The flag server now returns {"editRemovalCap":3000,"editRemovalVisibility":true,"enabled":"enabled","envOnboarding":true,"gitStatusType":true,"gitStatusUploads":false,"jsonlTranscript":true,"modelByMainModel":{"claude-haiku-5-5":"claude-sonnet-5[1m]","claude-haiku-5-5[1m]":"claude-sonnet-5[1m]"},"outcomeVisibility":false,"repoVisibility":true,"sameTurnSiblingContext":true,"severityByModel":{"claude-opus-4-8":{"t1":45,"t2":35},"claude-opus-4-8[1m]":{"t1":45,"t2":35},"claude-sonnet-5":{"t1":25,"t2":35},"claude-sonnet-5[1m]":{"t1":25,"t2":35}},"severityBySite":{"compactFabCheck":"on","handoff":"on","investigator":"on","sandboxNetwork":"on","workflowGate":"on"},"twoStageClassifier":true} for tengu_auto_mode_config, read as this account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
A small documentation edit on Speed up responses with fast mode touched a line naming /fast after this was published.