Source Intelligence
Follow Discord

DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

← All of v2.1.251 Home All releases ←olderv2.1.250
Claude Code v2.1.251

Second API routing path, off unless you turn it on

Use it now
Useful3 Signal4
API Routing Notable not in their notes

You can send API requests down a newer routing path by setting one of two environment variables.

Two alternate routing headers are selectable by env vars; without them nothing changes and both remote flags default off.

Feature flag
tengu_dreamy_frost Not enough to say

Nothing 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 v2.1.251: on

tengu_cedar_lattice Not enough to say

Nothing 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 v2.1.251: on

Read once, for one account on one subscription tier, against v2.1.251. It isn't a statement about your account. What a flag value here can and cannot tell you

CLAUDE_CODE_DISPATCH_V2DCLAUDE_CODE_DISPATCH_V2S
What

Outbound API requests can carry an anthropic-dispatch-id header selecting a newer routing path. Setting CLAUDE_CODE_DISPATCH_V2D (or the remote flag tengu_dreamy_frost) sends v2d; CLAUDE_CODE_DISPATCH_V2S (or tengu_cedar_lattice) sends v2s. With neither set no header goes out and the existing route is used. Both remote flags default off.

Details
  • The header is attached to real outbound requests, not just computed.
  • A cli_api_route_observed telemetry event fires once per process recording which route was actually taken.
Evidence

anthropic-dispatch-id

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.251 →