RIOT-2026.01 "GroundhogLoop" - Release Notes

RIOT is a multi-threading operating system which enables soft real-time
capabilities and comes with support for a range of devices that are typically
found in the Internet of Things: 8-bit and 16-bit microcontrollers as well as
light-weight 32-bit processors.

RIOT is based on the following design principles: energy-efficiency, soft
real-time capabilities, small memory footprint, modularity, and uniform API
access, independent of the underlying hardware (with partial POSIX compliance).

RIOT is developed by an international open-source community which is
independent of specific vendors (e.g. similarly to the Linux community) and is
licensed with a non-viral copyleft license (LGPLv2.1), which allows indirect
business models around the free open-source software platform provided by RIOT.

About this release

Here are some highlights of the 2026.01 "GroundhogLoop" release:

You can hack with RIOT on some new hardware! We now support yet another
ESP32-C3-based board: The Seeed Studio Xiao
ESP32-C3
with WiFi and Bluetooth capabilities, and a tiny form factor (#21829). RIOT can
now also drive the GP8XXX family of voltage and current DACs (#21182), as well
as the PMW3901 and PAA5100JE optical flow sensors (#21856).
RIOT developers now have a better way to interact with the system time via the
walltime module (#21343). This enables writing applications independently of
the RTC peripheral, as well as subscribing to time changes. Check out the
module documentation.
RIOT's build system now allows modules that use event threads to declare
special stack size requirements without conflicting with other modules (#21941).
For details on how to use this for your modules, visit the documentation
page.
When accessing crypto primitives via the PSA API, monocypher's Ed25519 is now
the default software backend, providing a much faster implementation out of the
box (#21821).
Given the success and steady growth of our new guide site, it can now be
accessed directly via https://doc.riot-os.org/, while RIOT's API documentation
(Doxygen) is still available at https://api.riot-os.org/ (#21968).
Nanocoap has undergone some work to decouple its API from UDP, with the
ultimate goal of easily supporting other transports in the future. Make sure to
check the latest version of
the documentation, as some
breaking changes have been made (#20900).

135 pull requests, composed of 250 commits, have been merged since the
last release, and 6 issues have been solved. 28 people contributed with
code in 64 days. 1551 files have been touched with 15841 (+) insertions and
11952 deletions (-).

Notations used below

+ means new feature/item
* means modified feature/item
- means removed feature/item

New features and changes

Core

core/lib/clist: fix example of clist_foreach usage in docs (#21848)

System Libraries

sys/psa_crypto: add monocypher as ed25519 software backend (#21822)
sys/walltime: add module for system time (#21343)
sys/ztimer/xtimer_compat: provide more fallback options (#20494)

sys/event: manage event thread size via build system (#21941)
sys/psa_crypto: unify buffer size size handling for ed25519 backends (#21821)
sys/suit: write size in suit_worker_try_prepare() (#21913)
sys/usb/cdc_acm, sys/tsrb: speedup usb_cdc ringbuffer handling (#21788)
sys/usb/cdc_acm: don't generate flush event when disconnected (#21914)

Networking

gnrc, nimble/ble: notify network layer of BLE connection events (#21608)
gnrc/rpl: float DODAG during local repair (#21816)
pkg/lwip: add LWP_IP4_ADDR_INIT macro (#21969)
sys/shell: add shell wrapper for openthread cli (#21862)

nanocoap: use default blocksize2 in coap_block2_init() (#21952)

Boards

boards/seeedstudio-xiao-esp32s3: Add Initial Support [new PR] (#21829)

boards/nucleo-wl55jc, cpu/stm32: enable RTC support, increase RTC
accuracy (#21837)
boards: migrate ESP32 based boards to common board module system (#21835)
boards: use boards.h to indicated UF2 bootloader usage (#21956)

CPU

cpu/native: introduce periph_i2c_mock (#20430)

cpu/esp32: fix compilation for GCC 15.2 on ESP32x RISC-V SoCs (#22017)
cpu/native,core: better contain ugly hacks (#21955)
cpu/sam0_common: clear tamper wake on gpio_irq_disable() (#21846)
cpu/{sam0_common,stm32}: Provide SVD_VENDOR and SVD_MODEL (#21872)
dist/tools/PyCortexMDebug: Integrate GDB extension into RIOT (#21863)
treewide: remove various deprecated macros and functions (#21985)

Device Drivers

drivers/gp8xxx: add initial support (#21182)
drivers/paa5100je: support for the PAA5100JE and PMW3901 optical flow
sensors (#21856)

drivers/slipdev: Refactor parser state machine for readability (#21953)

Documentation

doc/guides/advanced_tutorials: added event queue guide (#21899)
doc/guides: Add FileTree to Create Project Guide (#21948)
doc/starlight: add SECURITY.md (#21983)
.well-known/security.txt: Implement RFC 9116 (riot-os.org #156)

dist/tools,doc/doxygen: use doc-ci in the doccheck if possible,
update to Doxygen 1.15.0 (#21372)
doc/doxygen: remove deprecated pages (#21934)
doc/guides: document DOCKER_IMAGE environment variable (#21916)
doc/starlight: remove copy folder hacks (#21944)
doc: migrate file trees in guides to starlight TreeView component (#21946)
doc: reorder some drivers (#21943)
doc: use https://api.riot-os.org for API doc (#21968)
guides/build-system: document more targets (#21925)

Build System / Tooling

dist/tools/zsh-completion: Add completion for DOCKER_IMAGE and
OPENOCD_FTDI_ADAPTER (#21860)
tests/unittests: allow out-of-tree tests (#21328)

build: allow external module dirs with the same name when not
building in Docker (#21933)
dist/tools/dlcache: make script more portable (#21924)
dist/tools/edbg: bump version (#21858)
dist/tools/ethos: fix minor code quality issues (#21979)
dist/tools/tunslip: fix some minor code quality issues (#21977)
dist/tools/vera++: allow comments to be overlong (#21671)
makefiles/utils/test: remove explicit dependency on bash (#21917)

Examples

examples/lwip_ipv4: add example for LWIP IPv4 client/server (#21519)

Testing

tests/net: use random, free port for
socket_zep&gnrc_netif_ieeee802154 (#21853)

API Changes

drivers: rename ads101x driver to ads1x1x (#21731)
sys/net/*coap: Make APIs (more) transport agnostic (#20900)

Uncategorized

CODING_CONVENTIONS: add Section on Conditional Compilation (#21950)
release-notes.txt: add 2025.10 release notes (#21929)

.gitattributes: mark package-lock.json as binary (#21945)

And 26 minor changes.

Deprecations

Bug fixes (52)

core/lib/atomic_c11: Add __atomic_test_and_set() (#21883)
pkg/mpaland-printf: Add missing wrapper for fputs (#21889)
pkg: Add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to cmake flags (#21839)
pkg: Always add mandatory GITAMFLAGS (#21841)
board/esp32-ttgo-t-beam: small fixes (#21991)
boards/common/stm32: make stm32wl.cfg version agnostic (#21873)
build-system: fix RIOTBOOT_SKIP_COMPILE (#21938)
core/thread_flags_group: use portable implementation (#21895)
cpu/esp32/esp-idf: fix of a memory leak when using esp-now (#21975)
cpu/esp32: fix 6LoWPAN over BLE issue for ESP32-C3 (#21988)
cpu/esp32: fix esp_wifi stability problem by placing wdt_hal_*
functions in IRAM (#21980)
cpu/esp32: fix of a serious memory leak when using esp_wifi on
ESP32-S3 (#21974)
cpu/esp32: small doc fix (#21972)
cpu/esp8266: Fix crashes of the ESP866 when rebooting with or
disconnecting from WiFi (#22014)
cpu/esp8266: fix the crashes on startup in vendor code (#22010)
cpu/esp_common: fix FreeRTOS rmutex handling (#21926)
cpu/native: fix lockup on libucontext (#21915)
cpu/native: implement fputs and fwrite (#21912)
cpu/nrf5x_common: copy vendor files only when newer (#21868)
cpu/sam0_common/periph_i2c: reliably unstuck bus (#21891)
doc/guides/emulators: fix title headings (#21875)
doc/starlight: fix edit link for generated documents (#21987)
drivers/abp2: faulty saul init for multiple abp2 devices (#21852)
drivers/at86rf215: re-enable RPC when TX is done (#21849)
drivers/atwinc15x0: fix a potential buffer overflow on stack (#22041)
drivers/motor_driver: fix accidental braking (#21847)
drivers/mrf24j40: replace && with || in TX power validation (#21904)
drivers/periph/i2c: Replace LaTeX formula with static SVG file in
documentation (#21876)
drivers/sdmmc: fix stall in _disable_sd_clk (#21930)
drivers/sx126x: fix compilation for sx126x_dio3 (#21911)
drivers/sx126x: fix hardware detection on init (#21850)
drivers/sx126x: improve hardware detection (#21905)
gnrc_ipv6_ext_frag: fix some corner cases (#21937)
gnrc_sixlowpan_frag_sfr: check length before dispatching (#22027)
LICENSES: fix LGPL license text (#21864)
makefiles/tools/openocd-adapters: let OpenOCD auto-select transport (#21871)
pkg/cn-cbor: fix unaligned access (#21880)
pkg/lvgl: Fix configuration header and compilation issue (#22005)
pkg/lwip: fix dependencies when LWIP IPv4 and LWIP_DHCP is used (#21869)
pkg/tinydtls: various bugfixes (#21827)
rust: Update riot-sys selectively to fix C2Rust incompatibility (#21867)
SECURITY.md: Update public PGP key (#21981)
static-test: Check for Makefile.dep touching CFLAGS (#21965)
sys/event: fix stack size requirement build system integration (#21957)
sys/net/gnrc/netif: hold packets after tx_sync split (#21855)
sys/usb/cdc_acm: fix garbage input when disconnected (#21890)
tests: fix SPDX license tags (#21909)
tests: gnrc_ipv6_ext_frag: various fixes (#21935)

Known issues

Network related issues (54)

6lo: RIOT does not receive packets from Linux when short_addr is set (#11033)
Address registration handling inappropriate (#15867)
app/netdev: application stops working after receiving frames with
assertion or completely without error (#8271)
at86rf2xx: Dead lock when sending while receiving (#8242)
cpu/esp8266: Tracking open problems of esp_wifi netdev driver (#10861)
DHCPv6 client: Handling of NotOnLink incorrect (#20349)
dist/tools/sliptty/start_network.sh: IPv6 connectivity is broken on
PC (#14689)
driver/mrf24j40: blocks shell input with auto_init_gnrc_netif (#12943)
drivers/at86rf215: Incorrect channel number set for subGHz (#15906)
DTLS examples cannot send message to localhost (#14315)
Emcute cannot create a double-byte name (#12642)
ethernet: Missing multicast addr assignment (#13493)
ethos: fails to respond to first message. (#11988)
ethos: Unable to handle fragmented IPv6 packets from Linux kernel (#12264)
example/gnrc_border_router cannot answer after some time (#19578)
examples/cord_ep: Dead lock when (re-)registering in callback
function (#12884)
examples/gnrc_border_router: esp_wifi crashes on disconnect (#14679)
Forwarding a packet back to its link layer source should not be
allowed (#5051)
gcoap example request on tap I/F fails with NIB issue (#8199)
gcoap: Suspected crosstalk between requests (possible NULL call) (#14390)
Global IPv6 addresses remain deprecated after receiving RA (#19846)
gnrc ipv6: multicast packets are not dispatched to the upper layers (#5230)
gnrc/ipv6: "invalid payload length" - corrupted IPv6 header when
ENABLE_DEBUG=1 in mbox.c (#20390)
gnrc_border_router stops routing after a while (#16398)
gnrc_border_router: Kconfig and C disagree about number of addresses
per interface (#19947)
gnrc_icmpv6_echo: flood-pinging another node leads to leaks in own
packet buffer (#12565)
gnrc_ipv6: Multicast is not forwarded if routing node listens to the
address (#4527)
gnrc_netif_pktq leaks memory (#17924)
gnrc_rpl: missing bounds checks in _parse_options (#16085)
gnrc_rpl: nib route not updated when topology / DODAG changes (#17327)
gnrc_rpl: takes unusually long time to start routing packets (#19147)
gnrc_sock_udp: Possible Race condition on copy in application buffer (#10389)
gnrc_tcp: gnrc_tcp_recv() never generates -ECONNABORTED (#17896)
ieee802154_submac: IPv6 fragmentation broken (#16998)
LoRaWan node ISR stack overflowed (#14962)
LWIP TCP Communication Error (#19676)
lwip, submac: deadlock on user transmission (#21843)
lwip_sock_tcp / sock_async: received events before calling
sock_accept() are lost due to race condition. (#16303)
Missing drop implementations in netdev_driver_t::recv (#10410)
Neighbor Discovery not working after router reboot when using SLAAC (#11038)
netdev_ieee802154: Mismatch between radio ll address and in memory
address (#10380)
nrf52: Not able to add global or ULA address to interface (#13280)
nrfmin: communication not possible after multicast ping with no
interval (#11405)
ping6 is failing when testing with cc2538dk (#13997)
pkg/lwip: race condition (data loss) in async connection setup (#21874)
pkg/tinydtls: auxiliary data API does not work for async sockets (#16054)
Removing a TNT global address then adding a new one does not work (#20318)
samr30 xpro doesn't seem to use its radio ok (#12761)
scan-build errors found during 2019.07 testing (#11852)
stale border router does not get replaced (#12210)
test/lwip: enabling both, IPv4 and IPv6, results in unexpected
behavior (#18097)
tests/lwip: does not compile for IPv4 on 6LoWPAN-based boards. (#17162)
two nodes livelock sending neighbor solicitations back and forth
between each other (#16670)
xbee: setting PAN ID sometimes fails (#10338)

Timer related issues (5)

misc issues with tests/trickle (#9052)
periph/timer: timer_set() underflow safety check (tracking issue) (#13072)
periph_timer: systematic proportional error in timer_set (#10545)
saml21 system time vs rtc (#10523)
sys/newlib: gettimeofday() returns time since boot, not current wall
time. (#9187)

Drivers related issues (14)

at86rf2xx: Simultaneous use of different transceiver types is not
supported (#4876)
cpu/msp430: GPIO driver doesn't work properly (#9419)
drivers/at86rf215: not returning RX/IDLE after a while of operation
with RPL/UDP (#21685)
drivers/at86rf215: The activation of the address match interrupt is
missing in the at86rf215_reset function (#20505)
drivers/mpu9x50: regression (#21663)
examples/dtls-wolfssl not working on pba-d-01-kw2x (#13527)
fail to send data to can bus (#12371)
mdt_erase success, but vfs_format resets board (esp32-heltec-
lora32-v2) (#14506)
periph/spi: Switching between CPOL=0,1 problems on Kinetis with
software CS (#6567)
periph: GPIO drivers are not thread safe (#4866)
PWM: Single-phase initialization creates flicker (#15121)
STM32: SPI clock not returning to idle state and generating
additional clock cycles (#11104)
TCP client cannot send read only data (#16541)
tests/periph_flashpage: unexpected behavior on nucleo-l4r5zi (#17599)

Native related issues (5)

examples/micropython: floating point exception while testing on
native (#15870)
native not float safe (#495)
native: tlsf: early malloc will lead to a crash (#5796)
VFS_READ show correct data on every SECOND request only (#21470)
ztimer doesn't wake up on native if the pm_layered module is used (#21083)

Other platforms related issues (12)

Failing tests on FE310 (Hifive1b) (#13086)
[TRACKING] Fixes for automatic tests of ESP32 boards. (#12763)
boards/hifive1: flashing issue (#13104)
cpu/sam0: flashpage write / read cycle produces different results
depending on code layout in flash (#14929)
esp32-wroom-32: tests/netstats_l2 failing sometimes (#14237)
gcoap/esp8266: Stack overflow with gcoap example (#13606)
Interrupt callback function is instantly called on samd51 after
setting it from within interrupt callback function (#19861)
MPU doesn't work on cortex-m0+ (#14822)
newlib-nano: Printf formatting does not work properly for some
numeric types (#1891)
periph_timer: Test coverage & broken on STM32F767ZI (#15072)
riscv: ISR stack is too small for ENABLE_DEBUG in core files (#16395)
stm32f7: Large performance difference between stm32f746 and stm32f767 (#14728)

Build system related issues (7)

Build dependencies - processing order issues (#9913)
dist/tools/cppcheck/cppchck.sh: errors when running with Cppcheck
1.89 (#12771)
EXTERNAL_MODULE_DIRS silently ignores non-existent entries (#17696)
Kconfig: Unable to set Kconfig boolean variables with default true to
false (#21785)
make: ccache leads to differing binaries (#14264)
make: use of immediate value of variables before they have their
final value (#8913)
makefiles: make term does not print stderr output of child
process. (#21808)

Other issues (74)

[nRF5x] periph_uart unreliable with GCC 9.3.1 (#21842)
[tracking] Bugs found by the peripheral selftest (#20071)
[Tracking] Failures found with testing on real hardware for release (#21882)
[Tracking] Fix failures of test-on-iotlab (#20791)
[TRACKING] sys/shell refactoring. (#12105)
[tracking] unnecessary use of floating point arithmetic (#19614)
_NVIC_SystemReset stuck in infinite loop when calling pm_reboot
through shell after flashing with J-Link (#13044)
make term no longer works with JLinkExe v6.94 (#16022)
at86rf215 stops receiving until sending a packet (#19653)
b-l072z-lrwan1: tests/ztimer_overhead: test failure (#19224)
backport_pr: Only works for when fork is in user (not in
organization) (#18486)
benchmark_udp: hammering with low interval causes issues (#16808)
boards/esp32-wroom-32: tests/mtd_raw flakey (#16130)
Builds fail when different execstack options are around in objects (#18522)
Can't build relic with benchmarks or tests (#12897)
CC2538-CC2592EM has a very weak transmit power (#17543)
cpp: Exception handling undefined (#17523)
cpu/stm32: some tests are failing on CM33 (l5, u5) (#17439)
doc/boards: information concerning access to RIOT shell (#17453)
doxygen: CSS hack to hide doc breaks on older browsers (#21312)
edbg: long lines flooded over serial become garbled (#14548)
examples / tests: LoRa tests fail on platforms that don't support
LoRa (#14520)
examples/gcoap: client broken (#19379)
flashing issue on frdm-k64f (#15903)
frdm-k22f failing tests/periph_flashpage (#17057)
frdm-k22f fails tests/periph_timer (#19543)
Freeze into semtech_loramac_send call (pkg/semtech-loramac) (#18790)
gcoap: gcoap_req_send and related should return negative for errors (#19393)
gnrc_ipv6_nib: Neighbor Solicitation ping-pong (#18164)
I2C Crashes Kernel on Raspberry Pi Pico (#21187)
ieee802154_security: Nonce is reused after reboot (#16844)
kconfiglib.py choice override of menuconfig bug (#19069)
LVGL tests produce unaligned code, fail to build (#20110)
lwip: drivers/at86rf2xx/at86rf2xx_netdev.c invalid state during TCP
disconnect (#17209)
lwip: invalid state transition on ieee802154_submac users (#17208)
Making the newlib thread-safe (#4488)
mcuboot: flashes but no output (#17524)
MTD is confusing (#17663)
openDSME example application does not work reliable out of the box
with nRF52840 MDK Dongles (#21922)
Order of auto_init functions (#13541)
periph_rtt: rtt_set_alarm() blocks IRQ for 80 plus usec on STM32 (#19520)
pkg/tinydtls: Multiple issues (#16108)
Potential race condition in compile_and_test_for_board.py (#12621)
RIOT is saw-toothing in energy consumption (even when idling) (#5009)
riotboot: ECC faults (eg. in STM32L5 or STM32WB) not handled
gracefully (#17874)
rpl, rpble: handle closed connection to parent(s) (#21574)
rust-gcoap example is incompatible with littlefs2 (#17817)
Samr30/gpio: Erasing then write mux can generate spurious IRQ (#19993)
samr34-xpro: some tests failing (#19223)
sock_dtls: unable to send big messages (#17996)
spurious IRQs in periph_timer (#18976)
stdio UART input truncated (#21564)
stdio_ethos: infinite shell loop (#17972)
stdio_tinyusb_cdc_acm hangs with picolibc (#19277)
STM32 Nucleo boards improperly clocked (#19778)
STM32F4-discovery + mrf24j40 not working (#19711)
sys/riotboot: documentation issues (#11243)
sys/usb/usbus/cdc/ecm: interface thread blocked when connected host
interface is down (#21098)
tests/lwip target board for python test is hardcoded to native (#6533)
tests/periph_flashpage: failing on stm32l475ve (#17280)
tests/pkg/relic is failing on samr21-xpro when built using llvm (#19903)
tests/pkg_libhydrogen: test fails on master for the samr21-xpro with
LLVM (#15066)
tests/pkg_libschc: Failing test_reassemble_success_ack_always (#19445)
tests/riotboot does not pass on iotlab-m3 (#22006)
tests/test_tools: test fails while testing on samr21-xpro/iotlab-m3 (#15888)
tests: broken with stdio_rtt if auto_init is disabled (#13120)
tests: some tests don't work with newlib lock functions. (#12732)
tracking: failing tests with stdio_cdc_acm (#21231)
Types in byteorder.h need a cleanup (#14737)
USB identifiers with funny characters create mojibake (#17776)
usbus/msc: wrong error handling and behavior after usb reset (#19478)
Use of multiple CAN bus on compatible boards (#14801)
ztimer is incompatible with real-time requirements (#18883)
ztimer_periodic: occasional lockups (#21374)

There are 171 known issues in this release

Fixed Issues since the last release (2025.10)

esp32s2: xQueueGenericCreate() fails assertion due to failed
malloc() after ~2h (#21923)
esp32*: esp_now: failed assertion in xSemaphoreTakeRecursive() when
switching channel (#21919)
esp8266 crashes on WiFi disconnect (#21558)
gnrc_rpl: old routes are not deleted (#19423)
examples/gnrc_border_router: esp_wifi_init failed with return value
257 on ESP32-C3 with nimble_rpble (#19319)
add periph_rtc to STM32WL cpu and boards (#18789)
gomach: Resetting netif with cli doesn't return (#10370)

7 fixed issues since last release (2025.10)

Acknowledgements

We would like to thank all companies that provided us with hardware for porting
and testing RIOT. Further thanks go to companies and institutions that
directly sponsored development time. And finally, big thanks to all of you
contributing in so many different ways to make RIOT worthwhile!

More information

http://www.riot-os.org

Discussions

Join the RIOT Matrix room at: #riot-os:matrix.org
Join the RIOT Forum at: forum.riot-os.org
Follow us on Mastodon: floss.social/@RIOT_OS

License

The code developed by the RIOT community is licensed under the GNU Lesser
General Public License (LGPL) version 2.1 as published by the Free Software
Foundation.
Some external sources and packages are published under a separate license.

All code files contain licensing information.

Release-2026.01