Draft changelog: streaming latency and webhook auth updates

[mintlify]

Summary

Adds a Sep 5, 2026 changelog entry covering product changes shipped since the Sep 1 entry.

Changes

• Faster streaming delivery: hydrated streaming endpoints (including Filtered Stream) improved from ~6-7s to ~4-5s P99 latency.
• Expanded authentication: webhook management (/2/webhooks) and X Activity subscription management (/2/activity/subscriptions/{subscription_id}) endpoints now accept OAuth 2.0 and OAuth 1.0a user-context auth in addition to app-only Bearer Token.

Context

No PRs were merged since the last changelog entry. Changes were sourced from the streaming latency update commit and the OpenAPI spec sync commits merged to main this week.

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Project	Status	Preview	Updated
x-corp	🟢 Ready	View Preview	Sep 5, 2026, 8:09 PM

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