Sourced from com.squareup.okhttp3:mockwebserver's changelog.

Version 5.1.0

2025-07-07

• New: Response.peekTrailers(). When we changed Response.trailers() to block instead of throwing in 5.0.0, we inadvertently removed the ability for callers to peek the trailers (by catching the IllegalStateException if they weren't available). This new API restores that capability.

• Fix: Don't crash on trailers() if the response doesn't have a body. We broke [Retrofit] users who read the trailers on the raw() OkHttp response, after its body was decoded.

Version 5.0.0

2025-07-02

This is our first stable release of OkHttp since 2023. Here's the highlights if you're upgrading from OkHttp 4.x:

OkHttp is now packaged as separate JVM and Android artifacts. This allows us to offer platform-specific features and optimizations. If your build system handles [Gradle module metadata], this change should be automatic.

MockWebServer has a new coordinate and package name. We didn’t like that our old artifact depends on JUnit 4 so the new one doesn’t. It also has a better API built on immutable values. (We intend to continue publishing the old okhttp3.mockwebserver artifact so there’s no urgency to migrate.)

Coordinate	Package Name	Description
com.squareup.okhttp3:mockwebserver3:5.0.0	mockwebserver3	Core module. No JUnit dependency!
com.squareup.okhttp3:mockwebserver3-junit4:5.0.0	mockwebserver3.junit4	Optional JUnit 4 integration.
com.squareup.okhttp3:mockwebserver3-junit5:5.0.0	mockwebserver3.junit5	Optional JUnit 5 integration.
com.squareup.okhttp3:mockwebserver:5.0.0	okhttp3.mockwebserver	Obsolete. Depends on JUnit 4.

OkHttp now supports Happy Eyeballs ([RFC 8305][rfc_8305]) for IPv4+IPv6 networks. It attempts both IPv6 and IPv4 connections concurrently, keeping whichever connects first.

We’ve improved our Kotlin APIs. You can skip the builder:

val request = Request(
  url = "https://cash.app/".toHttpUrl(),
)

OkHttp now supports [GraalVM].

Here’s what has changed since 5.0.0-alpha.17:

... (truncated)

• d2dd180 Prepare for release 5.1.0.
• 61a8735 New Response.peekTrailers() API (#8921)
• 6684401 Update dependency gradle to v8.14.3 (#8915)
• 7adb2b6 Update junit-framework monorepo (#8914)
• e41ff18 Link to new mockwebserver artifacts (#8911)
• 0ff8751 Remove Graal init tracing (#8909)
• b9a2560 Run graal on master (#8907)
• 8339524 Remove ExperimentalOkHttpApi references (#8908)
• ce29ef6 Fix graal tests (#8906)
• 8579689 Don't force a response body read on all trailers (#8904)
• Additional commits viewable in compare view

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