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fix(blog): remove retired QUIC 0-RTT claim from why-now - #242

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Sep 18, 2026
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The why-now transport section claims decdn uses QUIC 0-RTT ("sends application data in the first packet… collapses discovery to one-way RTT… we use 0-RTT on cdn/probe/v1 and cdn/dht/v1"). That is not how decdn works.

Per the canonical design: every connection completes a full TLS 1.3 handshake — decdn deliberately does not use 0-RTT. Cold-start latency is bounded instead by concurrent probing (a ~500 ms probe-collection window with early exit) plus connection reuse and QUIC stream multiplexing (ADR 001 §Probe response collection, ADR 005 §Connection Management). There is also no ADR 015.

This rewrites the bullet to describe the real mechanism and says explicitly that decdn does not use 0-RTT. Prose-only change to one published post.

The matching internal draft is corrected in decdn/internal#130.

Follow-up (not in this PR)

0-RTT / ADR 015 also still appears in website/docs/overview/design-decisions.mdx (the design-decisions table) and in several decdn/internal fundraising materials (one-pagers, presskit, Product/client-cujs.md) already tracked as "needs ADR reconciliation." Happy to sweep those separately if you want.

🤖 Generated with Claude Code

The transport section claimed decdn uses QUIC 0-RTT on cdn/probe/v1 and
cdn/dht/v1 and "collapses discovery to one-way RTT." That is not how decdn
works: every connection completes a full TLS 1.3 handshake. The cold-start
cost is bounded by concurrent probing (a ~500ms collection window with early
exit) plus connection reuse and QUIC stream multiplexing, per ADR 001/005.

Rewrite the bullet to describe the actual mechanism and state explicitly that
decdn does not use 0-RTT.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Copilot AI lite review requested due to automatic review settings September 18, 2026 10:49
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🟢 Approval recommended

The change is a targeted prose correction, with only a minor grammar nit noted in the updated bullet.

Pull request overview

Updates the “Why Now” blog post’s transport section to remove an incorrect claim about using QUIC 0-RTT, replacing it with an accurate explanation of decdn’s latency characteristics (concurrent probing, bounded collection window, and connection reuse/stream multiplexing).

Changes:

  • Rewrites the QUIC bullet to describe concurrent probe fan-out and early-exit collection behavior.
  • Explicitly states that decdn completes a full TLS 1.3 handshake and does not use 0-RTT.
File summaries
File Description
content/blog/01-why-now.mdx Replaces the retired 0-RTT claim with prose describing concurrent probing + connection reuse over QUIC/TLS 1.3.
Review details
  • Files reviewed: 1/1 changed files
  • Comments generated: 1
  • Review effort level: Lite

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Comment thread content/blog/01-why-now.mdx Outdated
Comma after the introductory "For a CDN," and "once enough reply" ->
"once enough replies arrive" to fix the subject/number mismatch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
@alpergundogdu
alpergundogdu merged commit 54acbcc into main Sep 18, 2026
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@alpergundogdu
alpergundogdu deleted the blog-remove-0rtt branch September 18, 2026 11:07
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2 participants