Update changelog

docs/guides/changelog-quantum-compute-service.mdx

@@ -9,8 +9,21 @@ description: The latest updates from IBM Quantum Compute Service, including the
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 # IBM Quantum Compute Service
 
+Find the latest package release summaries and platform updates from IBM Quantum&reg; Compute Service on this page.
+
+<span id="platform-sep26"></span>
+## September 2026
+
+- **The first Nighthawk r2 QPU is now available** &mdash; Premium, Flex, and Pay-As-You-Go Plans now have access to `ibm_phoenix`, the first IBM Quantum Nighthawk r2 QPU and our fastest processor yet. `ibm_phoenix` is a high-connectivity, square-lattice 120-programmable-qubit device that delivers up to 25× higher throughput than Heron while matching its fidelity. 
+
+  The gains come from a newly introduced independent high-speed reset that returns every programmable qubit to the ground state faster and more completely. As a result, the default repetition delay is 1 µs (previously 250 µs), which pushes throughput above 100,000 Max Circuits Per Second (MCPS). For more about how IBM tracks quantum hardware performance across metrics of scale, quality, and speed, see [this blog](https://www.ibm.com/quantum/blog/hardware-metrics-2026).
+
+  The increased speed and connectivity make it possible to do more usable work from the same capacity, with the largest, most demanding workloads benefitting the most. Larger experiments, broader parameter sweeps, and methods that were once too costly at scale are now practical to run routinely.
+
+  `ibm_phoenix` is also built for the next era of quantum error correction research. Alongside high-speed reset, it supports mid-circuit reset and dynamic circuits for real-time control over error correction.
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-## August 2026
+## August 2026 
 
 - **Updates to IBM Quantum Platform** &mdash; A recent update to IBM Quantum Platform makes it easier to understand your job results, unlocks powerful new circuit design capabilities in Composer, and keeps you informed about your usage limits — so you can focus more on your quantum work.