Concurrent Session Detection / Claude Code v2.1.75

What

Claude Code now detects when multiple sessions are running simultaneously and offers a relevant tip.

Details

Sessions register PID files in the Claude Code data directory
When 2+ sessions are detected, a tip suggests: "Running multiple Claude sessions? Use /color and /rename to tell them apart at a glance."
Session count is also reported via telemetry (tengu_concurrent_sessions)

Evidence

Concurrent session tracking (search for "concurrentSessions", "color-when-multi-clauding")

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

The build it came inv2.1.75

13 Mar 2026 · 23 entries, this one is #6.

Either side of it

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Names in this entry

slash/color
Set the prompt bar color for the current session. Available colors: red, blue, green, yellow, purple, orange, pink, cyan. Use default to reset, or run with no argument to pick a random color. When Remote Control is connected, the color syncs to claude.ai/code. Also available in non-interactive mode (-p); requires Claude Code v2.1.205 or later
slash/rename
Rename the current session and show the name on the prompt bar. Without a name, auto-generates one from conversation history. Also available in non-interactive mode (-p); requires Claude Code v2.1.205 or later. From every rename surface, including claude.ai and the desktop app, Claude Code replaces control and invisible characters in the new name with spaces and caps the name at 200 characters. If the name is empty once invisible characters are removed, Claude Code rejects it and shows That name is empty once invisible characters are removed. Usage: /rename <name>. The character replacement and length cap require Claude Code v2.1.221 or later. If another live session on this machine already uses a name you pass, Claude Code applies a variant of it instead
flagtengu_concurrent_sessions
An analytics event, not a feature flag. Claude Code logs it at startup, after registering the session and counting the live sessions in its session registry, when that count is 2 or more; it carries num_sessions.

Is this right?

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