Draft changelog: Sep 6 streaming latency and webhook auth updates

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Summary

Adds a Sep 6, 2026 changelog entry covering product changes shipped this week.

Changes

• Faster streaming delivery: P99 latency on hydration-focused streams (including Filtered Stream) improved from ~6-7 seconds to ~4-5 seconds.
• Webhook management endpoints (/2/webhooks) and X Activity API subscription endpoints (/2/activity/subscriptions/{subscription_id}) now accept OAuth 2.0 and OAuth 1.0a user-context authentication, in addition to app-only Bearer Tokens.

Context

No PRs were merged since the last changelog entry (Sep 1). These changes shipped this week via the automated OpenAPI spec and docs updates on main. Internal-only churn (scope reordering, regenerated MDX stubs) was excluded.

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Project	Status	Preview	Updated
x-corp	🟢 Ready	View Preview	Sep 6, 2026, 2:14 AM

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